The prior art has already disclosed multilayer films which are permeable to UV radiation and inter alia can be used in the renovation of pipes.
By way of example, EP-A-0 342 897 describes a multilayer film which has a polyamide layer as a first surface layer and an ionomer sealing layer as a second surface layer. If the multilayer film is used for pipe renovation, the polyamide layer is bonded to a fibrous nonwoven by heating, and this is then saturated with a hardenable resin. After conditioning of the film, this is applied, together with the resin that, after the saturation process, is located on the surface, onto the region requiring renovation on the internal wall of the pipe, over the entire pipe circumference. After hardening of the resin by means of UV radiation, a stable pipe section at the internal pipe wall requiring renovation is obtained. The two ends of the film are then sealed to one another by way of the ionomer sealing layer.
In another known process for the renovation of subterranean pipes, a flexible insertion tube is provided, and is drawn into the pipe requiring renovation. Said insertion tube comprises two tubes, preferably plastics tubes, with different diameter, between which a support material saturated with a reactive synthetic resin has been introduced. After the introduction of the collapsed insertion tube into the pipe and inflation of the insertion tube to the diameter of the pipe, the synthetic resin is hardened between the two tubes in order to obtain, after removal of the internal tube, a stable pipe at the internal pipe wall requiring renovation. The hardening can be achieved via irradiation with UV radiation. In order to prevent undesired premature hardening of the synthetic resin prior to introduction into the pipe requiring renovation, it is necessary that the externally situated tube of the insertion tube has a protective layer or is composed thereof, in order to prevent premature exposure to external UV radiation and thus premature curing of the resin. In contrast, the internally situated tube of this type of insertion tube has to have permeability to UV radiation, in order to permit, in the inflated condition, the hardening procedure.
The internally situated tube of this type of insertion tube, or a corresponding multilayer film, preferably in the form of a tube, used for pipe renovation and as disclosed by way of example in EP-A-0 342 897, is subject to stringent mechanical requirements, in order that it can withstand loads arising during its handling, for example those occurring during introduction into the pipe requiring renovation, during the inflation of the respective film within the pipe, or—after successful renovation—during removal from the pipe.
A disadvantage of a multilayer film disclosed in EP-A-0 342 897 is that it has a point of weakness at least in the region of the seal seam, and/or a disadvantage with conventional tubular films which are used as internally situated tubes of an insertion tube during pipe renovation is that these do not have the mechanical properties required in order to withstand the loads described above. To this end, conditioning can optionally be used in order to achieve an improvement in conventional films, where these have at least one layer based on a polyamide.
There is therefore a need for multilayer films which do not have the abovementioned disadvantages.
It was therefore an object of the present invention to provide a multilayer film, in particular in the form of a tubular film, which is suitable as internally situated tube of an insertion tube for the renovation of subterranean pipes, preferably subterranean sewer pipes, since it has not only the necessary permeability to UV radiation but also mechanical properties that are sufficiently good for it to withstand the high loads that arise during pipe renovation.